This invention refers to a replaceable cartridge for a valve, comprising a cartridge cage, a supporting member for a hard material plate, a hard material plate mounted, operatively stationary, in said supporting member, and at least one sealing gasket interposed between said fixed plate and said supporting member. As well known, a cartridge of this kind further includes control means and at least one movable plate operatively connected to said control means and intended to displace contacting the fixed plate in order to regulate the mixing ratio of cold and hot water supplied to the valve, as well as the delivery rate of the mixed water.
In order that they may perform an effective closure and regulation, the fixed plate and the movable plate of a cartridge of this kind should be pressed the one against the other by an adhesion force proportionate to the pressure of the entering water, because in the contrary case the water pressure might take one plate out of the other, thus preventing their mutual cooperation; and moreover, a suitable force should be applied between the fixed plate and the respective supporting member, order to compress the gasket or gaskets interposed between these parts, to both purposes of ensuring the sealing action and of preventing the expulsion of the gasket or a deformation thereof in case that over pressures take place.
In most known constructions, the fixed plate simply rests on the respective supporting member, which consists in a seat offered by the cartridge cage itself or by a bottom applied to the cage. Both the adhesion force to be applied between the fixed plate and the movable plate, and the compression force to be applied to the gasket interposed between the fixed plate and the respective supporting member, are obtained by applying a force which presses the supporting member towards the movable plate, or vice-versa, whereby this force operates both between the supporting member and the fixed plate, thus compressing the gasket, and between the fixed plate and the movable plate, thus keeping them mutually adherent. A consequence, the adhesion force between the plates and the compression force applied to the gasket are equal to each other and to the applied force. Therefore, the applied force should be always at least equal to the greater of the two forces required for the stated purposes.
In most cases, the force required for compressing the sealing gasket and for keeping the same safety in its correct position is very much greater than the force required for operatively keeping at mutual contact the fixed plate and the movable plate, and therefore, in all such cases, between the plates there is applied a force unnecessarily great for its purpose. Such excessive force applied between the plates renders less sliding the control of the valve and causes unnecessary mechanical stresses of the component parts.
The Italian Patent No. 1,183,957 ( on which is based PCT/US 87/00542) of the same Inventor has proposed to provide retainment means arrange for connecting the fixed plate to the respective supporting member, with the gasket compressed therebetween, in such a way as to maintain between these parts a constraint state. Thanks to this arrangement, the compression applied to the sealing gasket of the fixed plate depends on the elastic characteristics of the gasket itself and on the geometrical characteristics of the gasket, the retainment means and the connected parts, and this compression is permanently maintained by the retainment means as a constraint force internal to the system formed by the foxed plate, the respective supporting member and the corresponding gaskets, and independent from the forces applied from the exterior to the fixed plate and its respective supporting member. Therefore it is possible to assign to these forces only the task of generating the operative adhesion needed between the fixed plate and the movable plate. The adhesion force between the plates may then be fixed or variable, but in any event it may be chosen by taking into account only the need for adhesion between the plates, irrespective of the need for compressing and retaining the gasket of the fixed plate.
However, the fact that the retainment means are provided to operate directly on the fixed plate in order to press the same against the respective supporting member implies that concentrated stresses are applied to the fixed plate. Because the plates are made of ceramic material or other hard and brittle material, the breakage of a relatively high percentage of plates is to be feared, at the time of mounting the cartridge or subsequently.